v3.26.1
Fair value - Summary of Fair Value Assets Measured on Recurring Basis, Significant Unobservable Input (Details)
$ in Thousands
Jun. 30, 2026
USD ($)
Dec. 31, 2025
USD ($)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value $ 6,161,975 $ 6,050,542
U.S. corporate    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value 2,776,874 2,810,727
Non-U.S. corporate    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value 849,991 783,056
Residential mortgage-backed    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value 358,002 349,333
Commercial mortgage-backed    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value 223,468 129,562
Fair value, recurring    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value 6,161,975 6,050,542
Fair value, recurring | U.S. corporate    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value 2,776,874 2,810,727
Fair value, recurring | Non-U.S. corporate    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value 849,991 783,056
Fair value, recurring | Residential mortgage-backed    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value 358,002 349,333
Fair value, recurring | Commercial mortgage-backed    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value $ 223,468 129,562
Level 3  | U.S. corporate | Internal models | Credit spreads | Minimum    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fixed maturity securities, measurement input (in basis points) 0.0014  
Level 3  | U.S. corporate | Internal models | Credit spreads | Maximum    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fixed maturity securities, measurement input (in basis points) 0.0166  
Level 3  | U.S. corporate | Internal models | Credit spreads | Weighted average    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fixed maturity securities, measurement input (in basis points) 0.0087  
Level 3  | Non-U.S. corporate | Internal models | Credit spreads | Minimum    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fixed maturity securities, measurement input (in basis points) 0.0081  
Level 3  | Non-U.S. corporate | Internal models | Credit spreads | Maximum    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fixed maturity securities, measurement input (in basis points) 0.0134  
Level 3  | Non-U.S. corporate | Internal models | Credit spreads | Weighted average    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fixed maturity securities, measurement input (in basis points) 0.0096  
Level 3  | Fair value, recurring    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value $ 262,841 258,913
Level 3  | Fair value, recurring | Internal models    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value 227,000  
Level 3  | Fair value, recurring | U.S. corporate    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value 182,720 197,721
Level 3  | Fair value, recurring | U.S. corporate | Internal models    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value 182,720  
Level 3  | Fair value, recurring | Non-U.S. corporate    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value 35,682 34,411
Level 3  | Fair value, recurring | Non-U.S. corporate | Internal models    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value 31,576  
Level 3  | Fair value, recurring | Residential mortgage-backed    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value 5,814 483
Level 3  | Fair value, recurring | Commercial mortgage-backed    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value $ 7,413 $ 7,467